Survey of maize differential gene expression upon environmental exposure to the tar spot pathogen, Phyllachora maydis

Authors: ROGGENCAMP, EMILY - Michigan State University; Jaiswal, Namrata; Helm, Matthew; THOMPSON, ADDIE - Michigan State University; CHILVERS, MARTIN - Michigan State University

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2025
Publication Date: 6/16/2025
Citation: Roggencamp, E.M., Jaiswal, N., Helm, M.D., Thompson, A., Chilvers, M.I. 2025. Survey of maize differential gene expression upon environmental exposure to the tar spot pathogen, Phyllachora maydis. PhytoFrontiers. https://doi.org/10.1094/PHYTOFR-12-24-0136-R.
DOI: https://doi.org/10.1094/PHYTOFR-12-24-0136-R

Interpretive Summary: Tar spot is one of the most important diseases of maize (corn) cause by P. maydis. Though this fungal pathogen is considered one of the most economically important diseases of maize, yet the exact steps taken by the pathogen to cause disease are not known. To begin to unravel this process, we prepared the gene expression profiles and compared the gene expression differences between non inoculated and tar spot inoculated maize B73 lines Over the course of disease development. RNA samples were collected at two timepoints, 10 days and 24 days after inoculation. Over 3000 genes were differentially expressed at both time points in tar spot inoculated plants. These genes are involved in defense response, photosynthesis, cell wall biogenesis, and plant secondary metabolite biosynthesis. Importantly, several maize genes previously implicated in having a role in tar spot resistance were found to be differentially expressed. Overall, this study provides a survey of B73 maize response to tar spot and identifies several genes that may be important in host-pathogen interactions and resistance mechanisms to tar spot disease.

Technical Abstract: Tar spot of maize, caused by Phyllachora maydis, is an emerging threat to crop production across the United States and Canada. Current effective management of the disease includes, in part, application of fungicides when warranted and planting of tolerant maize varieties as currently no commercial maize hybrids have complete resistance. Several studies have focused on mapping of tar spot resistant loci from various maize diversity panels resulting in candidate genes of interest. However, no further techniques have been performed for further understanding of the maize host defense response or resistant mechanisms to tar spot. In this study, the first differential expression analysis of maize in response to tar spot disease is presented. Potted B73 maize plants were exposed to infection by placing them into a tar spot infested maize field. Over the course of disease development, leaves were sampled at two timepoints: 10 days and 24 days post exposure. Differential expression was determined by contrasting the exposed samples to non-exposed controls at the respective timepoints. 3,160 genes were significantly differentially expressed at 10 days post exposure while 3,953 genes were significant at 24 days post exposure. These significantly differentially expressed genes (DEGs) were enriched in gene ontology biological processes and KEGG pathways involved in defense response, photosynthesis, cell wall biogenesis, and plant secondary metabolite biosynthesis. Importantly, several maize genes previously implicated in having a role in tar spot resistance were found to be differentially expressed. Furthermore, gene regulatory networks were constructed to gain insight into important gene regulators. This study provides a survey of B73 maize response to tar spot and identifies several genes that may be important in host-pathogen interactions and resistance mechanisms.